Compensating thermostat



Dec. 11, 1945. 1.. J KOCI 2,390,947

COMPENSATING THERMOSTAT Original Filed April 1 1940 C HIGH EXPANSION5/05 Z .5 31 1..|.|.\.. Ty

24 Z 25 O 2e Z6 DU D Patented Dec. 11, 1945 COMPENSATING THERMOSTATLudvik J. Koci, Chicago, Ill., asslgnor to Chicago Flexible ShaftCompany, Chicago, Ill., a corporation of Illinois Original applicationApril 1, 1940, Serial No.

Divided and this application October 25, 1943, Serial No. 507,530

2 Claims.

This invention relates to compensating thermostats and is a division ofmy application Serial No. 327,255, filed April 1, 1940, for Thermostats,which resulted in Patent No. 2,332,518, granted October 26, 1943.

The novel principle of said patent may be described thus: that if oneportion of a generally straight strip of unreversed bimetallic material(of any normal shape and variation in section modulus) is rigidlyfastened or restrained against both angular and translational motion anda second portion of the strip at a point longitudinally removed fromsaid first mentioned portion is subject to action including a reactivecouple or moment acting to restrain angular motion of said secondportion by permitting minimum restraint to translational motion of saidsecond portion in a direction normal to the general length of the strip,then said second portion will exhibit a thermostatic action in the lineof said direction but directed in one way or the opposite depending onwhether said second portion or the portion immediately adjacent to saidrigidly fastened portion, is heated. Said invention is claimedgenerically in said parent application and also claimed as to certainspecies which include the principle that the relative magnitude of thetwo opposite thermostatic actions above described can be varied byvariation of the effective section modulus of the strip or by othermeans which may serve to alter the degree of restraint to angular motionof said second portion.

The present invention has for its object the embodiment of the foregoingprinciple in a form characterized by a strip of thermostatic materialdiminishing in width from its central portion toward each terminal endtogether with means supporting each terminal end against both angularmotion and motion in a direction normal to the length of the strip,whereby to obtain a main response to the absolute temperature of aprimary medium surrounding the middle portion of the strip and tocompensate for temperature lags of the supporting terminal end portionsof the strip.

According to the present invention the thermostatic strip inherently hasconsiderable compensating'effect and this is of particular utility incertain applications wherein it is desired to obtain a. mainthermostatic response to the absolute temperature of a gaseous or fluidmedium surrounding the middle portion of the strip and to compensate forextreme temperature lags of the supported end portions.

5 normal to the general length of the strip.

Other objects and attendant advantages will be appreciated by thoseskilled in this art as the invention becomes better understood byreference to the following description when considered in connectionwith the accompanying drawing, in which:

Figure l is a plan view of a thermostat embodying the present invention;

Figure 2 is a side elevation of the structure shown in Figure 1;

Figure 3 shows an application of my invention in a thermostatic switchor means for making and breaking an electric circuit; and

Figure 4 is a side elevation showing a modified form of my inventionapplied in a. thermostatic switch.

Reference is made to the above mentioned patent for a furtherdescription of the novel principle first above described, whereby a mainthermostatic action in one direction and a compensating thermostaticaction in the opposite direction are obtained in a single strip ofnonreversed, non-reentrant, thermostatic material, to obtain a netthermostatic action in a direction In said patent I have used theterms Aeffect and B effect in explaining the thermostatic action; and theseterms will be used in a similar manner, hereinafter.

In Figures 1, 2, and 3 are; shown a diagrammatic embodiment of thepresent invention. Here, the letter C designates a frame structurehaving upstanding ends provided with coplanar slots D within which theend portions of a bimetallic strip K are positioned so as to be free tohave longitudinal movement but restrained against both angular andtranslational movement under temperature changes. The strip K preferablybut not necessarily of uniform thickness, is shaped so as to bediminishing in width from its central portion ll toward each terminalend l2, thereby providing tapered end portions H of decreasing graduatedrigidity. Assuming that the under side of the strip is the hightemperature side, if the strip is heated at its end portions as byconduction from the frame structure C, the central portion of the stripwill tend to move upwardly in the direction indicated by the end arrowsin Figure 2, this being the A eflect above mentioned; and conversely, ifthe central portion of the strip is heated to a temperature above thatof the end portions the strip will tend to move downwardly at thecentral portion in the direction indicated by the center arrow in Figure2, this being the B eliect" above mentioned. If-the thermostatic stripwere of uniform section modulus throughout its length a uniform changein temperature of the strip throughout its length would produce nolateral movement of the strip, that is, movement normal to the face ofthe strip, for the reason that the A and B effects would be equal andthe tendency of the middle portion of the strip to move down ward wouldbe exactly balanced by the tendency of the end portions to move themiddle portion upward. It will be seen that if one of these efiects canbe caused to predominate, the balance will be disturbed and the netmovement in one direction or the other with uniform change intemperature of the strip, can be produced. This net movement is theresultant thermostatic action in a direction normal to the generallength of the strip and may be described as the vector um of the A and Beffects.

Referring to Figure 2, I have illustrated graphically anddiagrammatically the thermostatic action when heat is applied todifferent portions of the strip along its length. For example, if themiddle portion of the strip at the section line is heated, say degrees,the middle portion of the strip will move downward in proportion to thewidth of the section diagram x at said section line 0. This is the Befiect. This effect diminishes as the point of heat application movestoward the left or the right; for example, if new a point at the sectionline I is heated 10, motion at the middle portion of the strip atsection line 0 will move downward an amount proportional to the width ofthe section diagram X at said section line I, and similarly if theportion at the section line 2 is heated 10 the resultant motion of themiddle portion of the stri will be less and of a magnitude correspondingto the reduced width of the diagram X at the section line 2. If now thestrip is similarly heated 10 at the section line 3, there will result nomotion of the middle portion of the strip, for the reason that thissection 3 is located at the nodal point of the diagram, that is, thepoint at which the thermostatic action reverses. If the strip is heated10 at the section line 4 the thermostatic action will be in the oppositedirection, that is, upward and of relative magnitude indicated by thewidth of the section diagram'Y at said section line 4. This descriptionas well as the diagram is theoretical for the purpose of illustratingthe principle; and it will be apparent that the width of the sectiondiagrams X and Y represents relative magnitude of deflection of thestrip at the middle point 0 in response to a unit rise in temperature atany given point along its length, also that the example of a unit riseof 10 at any given section line is theoretical because actually there isgradual heat conduction to ad: joining portions of the strip.

The diagram Figure 2 shows a very desirable characteristic of myinvention, namely, that of v a gradually reducing thermostatic responsein one direction, passing through a nodal point (i. e., the point of noresponse), and then into a gradually increasing response in the oppositedirection, considering the effect of the application of heat tosuccessive points along the length of the strip. This is of particularutility when compared with prior compensating thermostats; for example,prior instances of applying compensation usually have involved the useof a second thermostat distinct from the main thermostat and acting in adirection opposite from the main thermostat, or a second thermostatfastened to the otherwise free end of the main thermostat but reversedin the location of its high temperature side. If we consider the effectof the application of heat to successive points along the length of thelatter mentioned structure it would be apparent that as we proceed fromthe fixed end of the main thermostat strip we would obtain graduallydecreasing thermostatic action in one direction as far as motion of thefree end of the strip is concerned until we encounter the junction ofthe two strips at which there would be a very sudden transition tomaximum thermostatic action in the opposite direction followed bygradually decreasing thermostatic action in this same opposite directionas we approach the free end of this combination strip. As distinguishedfrom such prior structures, my invention locates that ortion of thethermostat having maximum primary thermostatic response closest to theregion of the temperature which it is desired to control and locatesthat portion of the thermostat possessing maxi- 'mum opposition orcompensating response in a region closest to that region whosetemperature variations it is desired to compensate. In practical casesthese two regions are seldom separated by an accurate dividing line orplane but gradually merge one into the other; and for this reason it ishighly desirable that the response of the remaining portions (i. e.,those possessing less than maximum response) of any compensatingthermostat shall show the same characteristic, that is, the gradualmerging of the main response into that of the secondary.

In Figure 3 I have shown the thermostatic strip K applied in athermostatic switch for controlling an electric circuit. This mountingof the strip K is the same as in Figures 1 and 2. A screw 23 threaded inthe frameportion C is arranged for adjustment to act as a stop to limitthe downward movement of the strip intermediate itsends, in thisinstance at the middle point. A lever 24 pivoted at 25 to an uprightportion l4 of the frame, carries a leaf spring 26 which extendsforwardly along the strip K and carries on its under side an insulationbutton 21 adapted to contact the strip and on its top side a contact 28positioned to engage a stationary contact 29 to control a circuit (notshown) for exercising a control function. A thumb screw 3| in the endportion l4 permits of adjustment of the position of the lever 24 and thespring 26 whereby to apply more or less lateral pressure on the stripand thus change the temperature at which the strip will act to flex thespring 26 and move the contact 28 into or out of engagement with thecontact 29. The stationary contact 29 alsoacts as a stop to limit theupward movement of the strip. Here, the thermostatic strip is mounted inthe same manner as in Figures 1 and 2 so that its end portions aresubject to angular restraint and to the reactive couple explained in myparent application, by permitting a limited amount of movement in adirection along the length of the strip in the slots D-D provided forreception of these ends. Theoretically, the thermostatic action is asdescribed above in reference to Figures 1 and 2. However, thisform islimited in its applications because of the resistance to sliding motionof the portions of the strip in the slots D-D. In actual practice Iprefer to rigidly clamp the end portions of the strip against bothangular and lon itudinal movement and to provide some degree of elasticsoftness in the longitudinal direction by corrugating the strip or bybuckling it as shown in Figure 4. In this form the strip K is supportedin a frame structure similar to that of Figures 1, 2, and 3, having acentral portion 43 provided with supporting abutments 44 and 45, againstthe upper surface of which are secured the end portions 01' the strip Kby suitable means such as large headed screws 46 and 41, the screwspassing through openin s 48 and 49, respectively. These screws serve tosecure the ends of the strip against the supporting abutments 44 and 45and to prevent relative angular movement of the ends of the strip. Herethe screws 46 and 41 fixedly clamp the terminal end portions and holdthe.

strip under lengthwise compression so that the intermediate portion ofthe strip is buckled, substantially as shown. With this constructionit-is possible to obtain friction-free snap acting operation of theswitch of a degree determined by the amount of longitudinal compressivestress to which the strip is subjected. In other respects thethermostatic switch of Figure 4 is the same as in Figure 3 and likereference numerals with prime marks are applied to like parts.

It is believed that this invention provides a compensating thermostatwhich is desirable from the viewpoint oi efliciency, dependability,accuracy, economy in cost of manufacture, and maximum freedom from theeti'ect of transient conditions. I

While I have described and illustrated specific embodiments of theinvention, this has been by way of illustration and not limitation, andI do not wish to be limited except as required by the prior art and theappended claims, in which I claim:

1. A thermostatic device for indicating or controlling the temperatureor a primary medium and tor compensating for the eii'ect of variati intemperature of an uncontrolled second medium, comprising a non-reversed,non-reentrant strip 01' thermostatic material, the strip diminishing inwidth from its central portion toward each terminal end whereby each endportion of the strip is of decreasing graduated rigidity, meanssupporting each terminal end of the strip against both angular motionand motion in a direction normal to its length, the entire length of thestrip intermediate the supported terminal ends being responsive totemperature changes throughout said length. said central portion beingprimarily responsive to the surrounding medium and thereby responding ina thermostatic action in one direction normal to the length of thestrip, said end portions of diminishing width being primarily responsiveto the temperature of said supporting means and thereby responding in athermostatic action opposite in direction from that of the firstdescribed thermostatic action, the thermostatic strip responding at itscentral portion in a net efiective thermostatic action which is thevector sum of the first and second described thermostatic actions andthus in the direction of that described thermostatic action whichpredominates, the described angular restraint being imposed directly bysaid terminal ends and directly through said end portions oi decreasingwidth, whereby to obtain a main response to the absolute temperature 01'said primary medium surrounding the middle portion of the strip and tocompensate for variations in temperature of the supporting means due tovariations in temperature of said uncontrolled second medium. I

2. A thermostatic device as set forth in claim 1, in which the endportions of the thermostatic strip are fixedly held in such manner as tocompressively stress the strip in a longitudinal direction so as toobtain snap-acting operation.

LUDVIK J. KOCI.

